Simple, handy hack from Flickr user Malowz to overcome the common autofocus problem many cameras have when shooting dark subjects. The lamp mounts on his camera’s hot shoe, and spotlights the subject when the shutter button is half-pressed, giving the autofocus plenty of light to work with, and then turns the lamp off, on the full press, for the duration of the exposure.
A common model wireless flash/shutter remote is used to relay the condition of the shutter button. The rest is surplus LED flashlight bits—a high-brightness LED, a small ready-made driver PCB, and a reflector. [Thanks, Udi!]